This application is a continuation of application Ser. No. 12/551,844, filed Sep. 1, 2008 now abandoned. The majority of all continuous filament fiberglass is made from E-glass and used in applications such as fiber reinforced plastics and non-woven mat for roofing reinforcement. Historically, E-glass was developed as a low electrical conductivity glass, giving it the “E” designation for “electrical”. To achieve low conductivity, the total alkali content, commonly designated as R2O (Na2O, K2O, and Li2O), had to be very low. The lack of R2O, which is a good flux, was compensated by a large percentage of alkaline earth oxide (CaO, MgO), which is a weaker flux. The composition was developed around a eutectic in the SiO2—Al2O3—CaO system. Some of the CaO was replaced by MgO, and B2O3 was added to help lower the viscosity. The resulting composition space, known as E-glass, has an ASTM specification, D-578-05, to designate the standard composition ranges, shown in Table 1. Early patents in this composition range were relatively high in B2O3 and include U.S. Pat. Nos. 2,334,961 and 2,571,074.
TABLE 1Weight %Printed CircuitBoards and AerospaceB2O3 5 to 10CaO16 to 25Al2O312 to 16SiO252 to 56MgO0 to 5Na2O + K2O0 to 2TiO2 0 to 0.8Fe2O30.05 to 0.4 F2 0 to 1.0GeneralB2O3 0 to 10CaO16 to 25Al2O312 to 16SiO252 to 62MgO0 to 5Total Alkali0 to 2TiO2 0 to 1.5Fe2O30.05 to 0.8 F2 0 to 1.0
Because of the very good water durability and fiberizability of E-glass, it became the composition of choice for general-purpose continuous filament glass fiber. The ASTM composition ranges, especially for general applications, are relatively wide, except for alkali (R2O), and can consist of glasses with a wide range of properties.
For E-glass, the most expensive raw materials are those that supply boron (such as borax, boric acid, Ulexite, and Colemanite) and these materials can comprise one-third or more of the total raw material cost even though the B2O3 content in the glass is below 10%. One factor adding to the cost of boron in E-glass is the very low alkali (R2O) content, which necessitates replacement of borax with higher cost boric acid unless colemanite is a viable alternative. The trend over the last several decades has been to reduce the B2O3 content in E-glass for raw material cost savings but the trade off typically comes in the form of higher melting temperatures and higher melt viscosity. Higher melt viscosity results in higher fiberization temperatures, represented by the temperature at which the viscosity of the melt is equal to 1000 poise and designated by Tlog3. An example of a low boron E-glass patent is U.S. Pat. No. 7,022,634 and an example of an essentially “boron-free” E-glass patent is U.S. Pat. No. 5,789,329.
The use of recycled glass, known as cullet, is common practice in glasses melted for production of insulation wool and glass containers, but not for E-glass. Cullet can be broken down into two categories: pre-consumer and post-consumer. The most common grade of pre-consumer cullet available is known as plate cullet, while the most common grade of post-consumer cullet is a mixture of green, amber, and flint (clear) crushed bottles, referred to as “three-mix”. The majority of commercially available pre-consumer and post-consumer cullet has 12-16% R2O, limiting the amount that could be used as a raw material for E-glass, due to the low total alkali metal oxides content of 0 to 2 weight % in E-glass formulations.
With the limit of 2% total alkali, E-glass produced with a three-mix cullet containing 13.9% R2O could only consist of a maximum of 11 weight % recycled content from the cullet. Glass recycling not only uses less energy than manufacturing glass from sand, limestone, and other processed minerals, but also saves emissions of carbon dioxide, a greenhouse gas.
Table 2 below sets forth example compositions of plate cullet and three-mix cullet.
TABLE 2Glass OxidesPlateThree-(weight %)CulletmixSiO272.472Al2O30.32.0Fe2O30.20.25B2O300Na2O13.813.2K2O0.080.7CaO9.310.7MgO3.60.8F200
It is an object of the present application to provide a glass composition which gives technologists greater flexibility in designing glass compositions for a wide range of glass properties and low cost production. More particularly, it is an object of the present application to provide a glass composition which allows for increased amounts of recycled glass, resulting in less greenhouse gas emissions and a decrease in the amount of material going to landfills.